Electrical apparatus



May 27, 1930 w. A. oLLlNs 1,760,837

ELEcTRIcAL APPARATUS Filed Sept. 13. 1928 INVENTOR MMM Patented May 27, 1930 UNITED STATES PATENT OFFHC IVILLIAM A. COLLINS, OF TOLEDO, OHIO, ASSIGNOR TO MOTO METER GAUGE & EXQUIP-k MENT CORPORATION, OF NEW YORK, N. Y., A CORPORATION F DELAWARE ELECTRICAL APPARATUS Application. filed September 13, 1928. Serial No. 305,823.

My invention relates to electrical apparatus, and is especially useful in connection with apparatus for indicating temperatureparticularly apparatus of the thermostatic rheostat type. However, the invention is not limited to use with thermostatic rheostats, but may be employed in any apparatus where a metallic brush is moved in opposite directions by means of a more or less delicate mechanism. I have found the invention to be peculiarly advantageous where thermal conditions in an automobile engine are to be indicated to the driver by electrical means.

Among the objects of my invention may be mentioned: the provision of means for effecting a large number of suitably graduated contacts in a comparatively small space, the provision of means for overcoming the retarding effect of brush friction upon se the contacts, elimination of the necessity for soldering the contacts, and prevention of the jumpy motion so often present where a brush moves over successive contacts. Other objects will later appear.

Perhaps the best known type of electrical apparatus in which my invention may be embodied is the thermostatic-rheostat for indicating temperature. Although the invention is not limited to use with such an apparatus, 3o its application to a thermostatic-rheostat will be explained by way of example.

In the drawings- Figure 1 is a longitudinal section through Y an apparatus constructed in accordance with SIS the invention,

Fig. 2 is an end view of the complete apparatus as seen from the left in Figure 1,

Fig. 3 is a view of the end opposite to that y shown in Fig. 2, andy 4 l Fig. 4 is an enlarged view of the brush and contacts.

Known forms of thermostatic-rheostats include an apparatus in which a metallic, graphite or other brush of conducting material is attached to a thermostat and wipes over electrical contacts as the thermostat is distorted by varying temperature. Varying resistance so caused in an electrical circuit affects a volt-meter which may be calibrated 59 to indicate temperature. In order to effect proper electrical connection between the brush and the contacts it is necessary that some friction exist between them. This friction retards the motion of the brush and of the thermostatic element in response to temperature changes. Thus the instrument will show too high a value if the temperature is falling, and too low a value if the temperature is rising as a result of friction retardation. TVV here accuracy is required such differences in reading are objectionable.

I have discovered that means may be provided which will cause the position of the brush upon the contacts to be the same for a given temperature regardless of whether that temperature succeeds a higher or a lower temperature. To this end I provide means for overcoming the friction of the brush when moving in one direction.

Referring now more particularly to the drawings, there is shown a hollow cylindrical tube 10, about which is tightly fitted a threaded bushing 11, adapted to screw into a wall 12 thus projecting the tube 10 to its other side where the temperature is to be measured. The end of the tube 10, farthest from the bushing 11 is closed by a plug 13. Carried by this plug 13 is a thermostat 14 formed in the usual way of two dissimilar metals. Also carried by the plug 13 is a spring 15 which is preferably made of phosphorbronze. Both the thermostat and the spring project completely through the tube to its other end. Attached to the spring 15, at the end which is remote from the plug 13, is a brush 16. Thus the spring 15 carries the brush 16. This brush rests upon contacts 17 whose formation and disposition will be subsequently described. The spring 15 is so constructed and attached to the plug 13 that it overcomes the friction of the brush when moving in one direction, and tends to hold the brush 16 against the contacts nearest the spring, in other words at one eXtreme of the contacts.

The thermostat carries at its free end a set screw 18, which is adjusted to contact with the spring 15 near the end at which the brush 16 is attached. The thermostat is so constructed and attached, and the set screw so adjusted that at normal temperature there will be no pressure by the set screw 18 against the spring.

A spool 19 of bakelite or other insulating material is attached around the tube 10 adjacent the bushing 1l, and on this spool is Wound a coil oi? resistancewire 2O which is in circuit with an electrical indicator (not shown). A part ot the tube end 21 is Vflared outward and a piece ot insulating material 22 is attached to its outer surface. Selected loops 28 are pulled out oi the coil 20 passed through openings in the flared edge 20 and looped over the insulating material S22. The insulation is removed from the outer parts ot these selected loops of Wire 23., and they thus form the contacts, tapping the resistance coil at different points, over which the brush 1G passes. By a suitable selection ot the loops which are pulled -from the coil 20, the resistance value of a given distance which the brush travels may be determined at will. By merely drawing the loops over a piece ot insulating material and then scraping oit the outer part ot the insulatio it is possible to dispense With the usual solderin or other fastening of the contacts over which a brush travels. It Will also be seen that by this method of attachment and by the elimination of soldering a greater number of contacts may be gotten into a given space than is possible otherwise.

The operation of the apparatus is best described in connection with a container' in which is carried a liquid Whose temperature is variable. The engine jacket of an ordinary automobile for instance, is such a container. Vith the bushing carrying the tube 10 screwed into the container Wall, the tube 10 Will assume practically the temperature of the liquid in the container. As this temperature rises, the thermostat 14 lexcs toward the contacts and the set screw 18 forces the spring 15 toward the contacts, thus moving the brush 16 across the contacts. Thus the thermostat upon iieXing opposes the spring 15 and moves the brush 16 toward the other eXtreme of the contacts from which the spring tends to hold it. In so doing the thermostat overcomes the brush friction upon the contacts and the opposition of the spring. The thermostat is therefore adapted to move the brush over the contacts in one direction and the extent of this movement Will depend upon the distortion ot' the thermostat, Which in turn depends upon the degree of temperature.

As the temperature falls the thermostat iieXes in the other direction-that is to say, away from the contacts-and the spring alone moves the brush back to its original position. Thus the thermostat overcomes both brush friction and spring tension when moving in one direction and merely diminishes the pressure of the set screw 18 upon the spring When moving in the other direction. As a result, With increasing temperature the thermostat operates the brush, and With decreasing temperature the spring alone operates the brush. As the brush Wipes across the contacts it either increases or decreases the amount of resistance in the indicating circuit. The complete instrument is connected in circuit through the container Wall 12 and a threaded pin 24, to which may be attached a Wire leading to the indicating instrument, which in turn may be grounded to the container Wall 12 thus completing the circuit.

The foregoing description has been given merely by Way of illustration. Obviously other embodiments of the invention Will readily occur to those dealing with the problem ot rheostat construction and the elimination of brush friction.

I claim In a temperature responsive apparatus, a resistance coil, contacts tapping said resistence coil at different points, and a brush adapted to make electrical connection with said contacts thus short-circuiting a part oit' aid resistance coil, in combination With a g carrying said brush adapted to hold said brush at one eXtreme oil" said contacts, and a bi-metallic thermostat in adjustable Contact with said spring adapted upon heating to flex, oppose said spring and move said brush toward the other eXtreme of said contacts.

1n testimony whereof I have signed my name to this speciiication.

VILLIAM A. COLLINS. 

